The present invention relates to an energy dispersive X-ray fluorescence thickness tester having the merits of multiple simultaneous elements and non-destructiveness used in thickness control in the surface treatment industry, such as plating or sputtering films.
Conventionally, with an energy dispersive X-ray fluorescence thickness tester, film formation for surface treatment is well known and used in a production line for the purpose of quality control. This means that there is a limitation that there is no time for measurement. Further, high counting efficiency becomes important due to the energy distribution, X-ray fluorescence thickness testers using a proportional counter are mainstream, and in the case of use for the purpose of research and development, accuracy and sensitivity are required due to the limitations with respect to measurement time, and X-ray fluorescence thickness testers fitted with Si (Li) semiconductor detectors having excellent energy resolution or PIN diode X-ray detectors are also used.
In an energy dispersive detector, regarding detection performance, resolution and counting efficiency are mutually incompatible. This means that generally if width and area of a sensor device is enlarged in order to improve counting efficiency, then resolution is impaired or no longer functions.
Conventionally, in the case of performing film thickness measurement with an X-ray fluorescence thickness tester, since a proportional counter is generally used, if there is separation to the extent of the atomic number of elements constituting a thin film or a material (substrate), accurate composite measurement is possible even without carrying out specialized processing, but nickel (z=28) and copper (z=29) that have atomic numbers next to each other in the periodic table of elements are separated, and are overlaid in order to count respective peaks. This means that either a secondary filter method is used to insert a cobalt (Z=27) thin plate in front of the detector to perform peak separation using a difference in absorption effect in the cobalt with respect to nickel and copper, or a digital filter method is used to mathematically perform peak separation from peak shapes. However, the secondary filter method is restricted in application combinations. If there is a dedicated machine then the secondary filter method is effective, but if the purpose is to measure various combinations this method can not be used. Also, the digital filter method can be applied to various combinations, but there is a problem with stability compared with the secondary filter method, accompanying peak separation errors.
If there are requirements for peak separation, it is possible to use an Si (Li) semiconductor detector having excellent energy resolution, but in order to use an Si (Li) semiconductor detector it is necessary to periodically supply liquid nitrogen as a cooling medium, and there is a problem with respect to cost and operability. Also, in order to solve the problem of liquid nitrogen supply, a PIN detector is adopted that degrades energy resolution but can be used with Peltier cooling. In this case, detection efficiency with respect to high energy X-rays is poor in principle, and this method is limited to low energy X-ray applications.
In low energy regions in the vicinity of X-ray energy, a PIN detector having excellent energy resolution is used, and in high energy regions where counting efficiency of a PIN detector is low, a proportional counter or CdZnTe detector having poor resolution but excellent counting efficiency is used, since there is no need for resolution.